The invention relates to a method used in an arrangement for image data compression by vector quantization in accordance with a precoding in blocks constituted by a plurality of picture elements, thereafter comparing by means of a neural network precoded blocks with reference words stored in the form of a code book in the neural network so as to transmit to a receiver selected indices corresponding to the index of the reference words nearest to the precoded block.
The invention also relates to a structure for image data compression utilizing a plurality of these arrangements.
A data compression arrangement of this type is disclosed in the document "Building a heirarchy with neural networks: an example--image vector quantization" L. D. JACKEL, R. E. HOWARD, J. S. DANKER, W. HUBARD and S. A. SOLLA. Applied Optics vol. 26 no. 23 Dec. 1987 p. 5081.
This document describes the use of a neural network effecting the coding of image data by vector quantization. It relates to high-definition television pictures with the object of effecting their digital transmission in real time. Taking account of the limited capacity of transmission channels, it is necessary to effect a data compression. To that end an image is precoded in blocks, each formed from a plurality of picture elements. To limit the quantity of data to be transmitted, each block is compared with a list of reference words (relating to reference blocks) placed in a code book and in accordance with a similarity criterion, a reference word is selected from the code book, which word is nearer to the block to be encoded and of which only the index is transmitted, thus rendering it possible to find it in the list of the same code book present at the receiver end.
In accordance with this document, this word recognition operation is effected with the aid of a neural network so as to render it possible to operate at the rate necessary for the encoding of a video image. This document utilizes a fixed code book which can be drawn up beforehand. It is then not necessary to base it on multiple image configurations.